This invention relates generally to the processing and purification of water and wastewater streams.
A significant fraction of housing units in the United States use onsite treatment of septic water incorporating as its basic treatment element the use of land processing and disposal. While such systems have included a variety of configurations and filtering media, almost all that have been sanctioned by state regulatory authorities involve the use of a septic tank and a soil filtering and absorption system in the form of a drainage field. Alternative use of sewer systems has been expensive and burdensome for many suburban and rural communities. Nevertheless, the need for and the construction of individual on-lot septic and wastewater treatment systems have been growing at a significant rate. Unfortunately, only about one-third of the available land area for such construction and use in the United States has soils that are suitable for onsite treatment systems. Moreover, in areas where there has been pressure for more housing, onsite systems have often been installed on land that is not suitable for conventional soil absorption systems. Contaminated wells attributed to inadequately treated septic tank effluent and nutrient enrichment of lakes from near-shore development are examples of what may occur when a soil absorption system is installed in an area with unsuitable soil or geological conditions. Also, because of the potential health hazards of improperly functioning systems, public health officials have sought methods that improve the performance of both new and existing onsite systems.
It would be beneficial to provide a system to treat septic waste from residences located in areas having institutional and environmental restrictions that do not allow or that limit the use of drainage fields and where there are no existing sewer facilities. Additionally, it would be beneficial to provide a system that produces an effluent stream having a purity level superior to that provided by the action of a conventional combination of septic tank systems that use properly configured drainage fields for final disposal.
The total amount of pollutant in residential septic discharges is usually less than 0.2% of the liquid stream, suggesting that there may be treatment methods that can concentrate or remove the relatively small amount of pollutant and leave the remaining water in a condition suitable for direct discharge into ground or surface waters, or even for reuse. Different techniques are available, including use of a variety of filters, chemical dosing, reverse osmosis, and evaporation. Some of these are either very pollutant specific or more expensive than employing the conventional use of septic tanks and drainage fields for use in areas having suitable soil characteristics. Some produce residual liquid streams containing concentrated quantities of contaminants that still require separate and additional treatment for subsequent and acceptable disposal.
Several septic treatment methods (such as those described in U.S. Pat. Nos. 6,872,313 and 6,942,800) discuss the introduction of air and even enzyme addition into septic tanks or reaction containers in order to cause or assist in aeration as a means to more completely process contaminants or even to eliminate the use of drainage fields. U.S. Pat. Nos. 6,982,037 and 7,517,454 describe the use of filtering and clarification to remove suspended particulate matter. Other methods, such as developed in U.S. Pat. No. 6,517,711 further extend the practical application of filtration by incorporating backwash capability presumably in order to reduce maintenance and filter replacement requirements. However, these may not always provide satisfactory purification results by themselves, particularly due to their failure in eliminating or even minimizing the content of dissolved solids and related ionic salts in their product water (effluent streams).
The use of evaporation or reverse osmosis treatment as employed for industrial wastewater processing or in desalination, has disadvantages when considered for residential application or for use in remote areas. Each produces a residual stream that must be disposed of in an alternative and often costly manner. Evaporation has been proven too complex for small systems and would require relatively large energy levels for its operation. It also would be susceptible to scaling conditions if a high water recovery level is to be used in an attempt to reduce the quantity of the rejected stream. Reverse osmosis processing would be more advantageous for small sized treatment systems since it would require lower energy requirements. However, it would still produce a non-permeate (reject) stream that would contain a concentrated level of dissolved solids. Thus, for this application, a reasonable alternative method of treatment is still needed that treats reject streams at low cost and with minimal operator attention.
Electrolytically-based processes appear to offer some advantages. These involve the passage of an electric current into the fluid via electrodes, which may be sacrificial in some configurations due to metal erosion by electrolysis action. Operating costs seem to be lower when compared to the use of chemical injection. U.S. Pat. No. 6,663,766 suggests and uses horizontally-placed electrode plates having misaligned flow passages in order to promote turbulence. Other attempts have been made to take advantage of the potential for using electrolytic processing of wastewater with some success (such as disclosed in in U.S. Pat. No. 5,531,865). Aluminum or iron electrodes are employed and the practice involves the introduction of direct current into the feed stream to energize the process. In such cases, the aluminum or iron goes into solution at the anode and gas (often hydrogen) may be released at the cathode. Trivalent metals used in the fabrication of anodes readily coagulate pollutants which can then be separated and removed by settling or filtration. Some of the problems encountered with this technique have been associated with electrode lifetimes as well as the need to employ relatively high electric current and attendant energy consumptive levels.
A modification used in the electrocoagulation process is one in which the gas generated by the electrolytic action in the water is used to capture the coagulated pollutants and float them to the water surface. This process is referred to as electroflocculation. This also does not require the use of chemicals, enabling such processing to achieve some of the desired operating goals. But, such use has often been configured as a batch-type process which causes concern when there is the need for unattended operation over long time periods in some applications, as well as possibly high replacement rate of electrodes, or the need to supply metal additives as the sacrificial material.
However, even this problem may be overcome by using variations in the electrolytic technique and equipment configuration. For example, U.S. Pat. No. 4,101,409 suggests the introduction of compressed air in order to assist in the flotation of suspended solids up to the water surface. This patent also reports that the simultaneous injection of air into the water could enhance the purification process. This seems to alleviate the need to employ large amounts of electrical energy to produce significant electrolytic off-gassing in promoting the agglomeration and flocculation process. Both organic and inorganic contaminants appear to be treatable in this manner, as well.
All references cited herein are incorporated herein by reference in their entireties.